Method for checking the operability of an ambient pressure sensor of an internal combustion engine

ABSTRACT

A method for operating an internal combustion engine is described, in which the ambient pressure is determined by an ambient pressure sensor and the pressure in an intake manifold of the internal combustion engine is determined by an intake manifold pressure sensor. In this method the reliability performance of the ambient pressure sensor is checked by comparing the ambient pressure to a starting value that is obtained by the intake manifold pressure sensor before a starting process of the internal combustion engine. The comparison is only performed if a preceding check of the intake manifold pressure sensor yields the result that it is operational.

FIELD OF THE INVENTION

The present invention is directed to a method for operating an internalcombustion engine, in which the ambient pressure is determined by anambient pressure sensor and the pressure in an intake manifold of thecombustion engine is determined by an intake manifold pressure sensor,and in which the reliability performance of the ambient pressure sensoris checked by comparing the ambient pressure to a starting value that isobtained before or during the starting process of the combustion engine.

BACKGROUND INFORMATION

Such a method is described in German Published Patent Application No.100 21 639. However, an additional signal may be required there, namelya modeled intake manifold pressure, in order to perform the check of theambient pressure sensor.

SUMMARY OF THE INVENTION

The present invention provides an example method for operating aninternal combustion engine, with which an easy and yet reliable check ofthe ambient pressure sensor may be provided.

According to an example embodiment of the present invention, in anexample method of the type named at the beginning, by performing thecomparison only if a preceding check of the intake manifold pressuresensor yields the result that it is operational.

According to an example embodiment of the present invention, it may beensured that the check of the ambient pressure sensor is only performedif the intake manifold pressure sensor has been recognized asoperational. If that is not the case, checking the ambient pressuresensor may not be possible. Thus, according to an example embodiment ofthe present invention this check is made dependent on one or morerelease conditions that must be fulfilled. This may ensure that thecheck of the ambient pressure sensor consistently yields a correctresult. Furthermore, because of the prior release conditions the entireexample method may remain simple and manageable.

Further features, possible applications, and advantages of the presentinvention derive from the following description of exemplary embodimentsof the present invention, which are illustrated in the figures. All ofthe features described or illustrated represent the object of thepresent invention per se or in any combination, regardless of theirsummary in the patent claims or their back-references and regardless oftheir wording in the description or illustration in the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic block diagram of an exemplary embodiment of aninternal combustion engine according to the present invention.

FIGS. 2 and 3 show schematic flow charts of an exemplary embodiment of amethod for operating the internal combustion engine of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 illustrates an internal combustion engine 10, which is intendedin particular for propelling a motor vehicle. Combustion engine 10 hasan intake manifold 11 and an exhaust pipe 12. A throttle valve 13 isinstalled in intake manifold 11. Ambient air is supplied to combustionengine 10 through intake manifold 11. The quantity of air supplied maybe influenced through throttle valve 13.

Positioned in intake manifold 11 downstream from throttle valve 13 inthe intake direction is an intake manifold pressure sensor 14, which isprovided for measuring the pressure in intake manifold 11. Outside ofintake manifold 11 there is an ambient pressure sensor 15 for measuringthe ambient pressure.

Intake manifold pressure sensor 14 produces a signal DSS, and ambientpressure sensor 15 produces a signal DSU. Both signals DSS, DSU are fedto an electronic control unit 16 which, depending in part on signalsDSS, DSU, controls and/or regulates the operating variables of internalcombustion engine 10.

To diagnose the reliability performance of ambient pressure sensor 15,the following example method is performed by control unit 16. Theexample method is stored as a computer program on an electric storagemedium, for example a flash memory, and is performed by a computer ofcontrol unit 16 by executing the individual program commands.

In this example method, release conditions are first checked, afterwhich, if the release conditions are fulfilled, the check of ambientpressure sensor 15 is performed. The check of the release conditions isexplained below on the basis of FIGS. 2 and 3. The check of ambientpressure sensor 15 takes place at the end in FIG. 3.

In FIG. 2 there is a bit C_ini, which has a positive slope when theignition of combustion engine 10 is first switched on. The positiveslope results generally in control unit 16 being initialized.Specifically, the positive slope of bit C_ini results in a flip-flop 21and a flip-flop 22 of FIG. 2 being reset.

Flip-flop 21 is set if a bit B_sta has a positive slope. This is thecase when a starting process of internal combustion engine 10 istriggered by control unit 16. This is the case if certain startingconditions are fulfilled. For example, a starting process may need tohave been initiated by the driver, an automatic transmission may berequired so be in “park,” and so on.

If flip-flop 21 has been set by bit B_sta, its output is HIGH.

Flip-flop 22 is set if the speed of internal combustion engine 10 iswithin a prescribed speed range. This speed range is oriented toward theactual speed that internal combustion engine 10 should have in thestarting process. The speed range is defined by an upper value NDDFM anda lower value NDDFA, which are present at a comparator 23. Comparator 23checks whether the actual speed nist of internal combustion engine 10 isbetween the two values NDDFM, NDDFA, and hence within the desired speedrange.

If flip-flop 22 has been set in this manner, a HIGH signal is present atits output, whose rising slope is relayed through a slope detector 24.

Actual angle wdk of throttle valve 13 is compared to a prescribedmaximum throttle valve angle WDKBAST by a comparator 25. If actual angleWDK is smaller than this maximum throttle valve angle WDKBAST, theoutput of comparator 25 is HIGH.

Actual duration tnst of the starting process is compared to a prescribedmaximum duration SY_TSIDSS by a comparator 26. If duration tnst isshorter than this maximum duration SY_TSIDSS, the output of comparator26 is HIGH.

The outputs of flip-flop 21, slope detector 24, and the two comparators25, 26 are sent to an AND gate 27. If all four inputs of AND gate 27 areHIGH, its output is also HIGH.

This is the case when i) the ignition of internal combustion engine 10is just turned on, ii) a starting process is triggered by control unit16, iii) the actual speed of internal combustion engine 10 is within adesired speed range, iv) throttle valve 13 is open no wider than themaximum throttle valve angle, and v) the starting process has not yetexceeded the prescribed duration.

This is a first part of the aforementioned release conditions that maybe required to be fulfilled for the check of ambient pressure sensor 15to be performed. If the conditions are fulfilled and the output of ANDgate 27 is HIGH, this is recognized by function 28 and is furtherprocessed as part of the measures identified with /1/, /2/, and /3/ inFIG. 2.

In measure /1/ a bit B_psidss, which indicates whether the check ofambient pressure sensor 15 may take place, is set to “true=one.” This isthe case when all release conditions are fulfilled and the output of ANDgate 27 is HIGH.

Measures /2/ and /3/ relate to intake manifold pressure sensor 14. Itssignal DSS is used by control unit 16 to produce a pressure psh inintake manifold 11.

Before a starting process of internal combustion engine 10, i.e., wheninternal combustion engine 10 is off, pressure psh in intake manifold 11and in particular also the pressure downstream from throttle valve 13 isapproximately the same as the ambient pressure because internalcombustion engine 10 is at rest. This is equivalent to pressure pshmeasured by intake manifold pressure sensor 14 before a starting processbeing approximately the same as the ambient pressure. This pressure pshmeasured by intake manifold pressure sensor 14 before the startingprocess may thus be used to diagnose ambient pressure sensor 15.

To this end, pressure psh measured by intake manifold pressure sensor 14before the starting process is stored by control unit 16 as startingvalue psh_sta. The storage process may be carried out until the startingprocess, in particular until power is supplied to the starter.

According to FIG. 2, current pressure psh in intake manifold 11 issubtracted from stored starting value psh_sta by a block 29. Thedifference is then compared to a prescribed minimum value DPDDF by acomparator 30. If the difference is smaller than minimum value DPDDF,the output of comparator 30 is HIGH.

In this check it may be assumed that the pressure in intake manifold 11drops sharply after the beginning of the starting process. Thus thedifference between current pressure psh and stored starting valuepsh_sta must be large. If this is the case, i.e., if minimum value DPDDFis exceeded, it may be concluded therefrom that intake manifold pressuresensor 14 is operational.

The HIGH signal at the output of comparator 30 results in bits B_sidssand B_drsidss being set to “true=one.” This is equivalent to a defect inintake manifold pressure sensor 14. If the output of comparator 30 isLOW, the forenamed bits are set to “false=zero,” which signals thereliability performance of intake manifold pressure sensor 14.

Bit B_sidss is intended to be further processed by control unit 16.Among other things, bits B_elm and E_ds, explained below, are based onthis bit B_sidss. Bit B_drsidss is stored, and may be used for examplein conjunction with an inspection or repair of internal combustionengine 10 to direct the testing personnel to the defective intakemanifold pressure sensor 14.

Let it be pointed out again that measures /1/, /2/, and /3/ are carriedout only if the described release conditions are fulfilled and theoutput of AND gate 27 is HIGH.

In FIG. 3 there is a flip-flop 31, which processes bits B_sta and C_iniin the same manner as explained earlier in connection with flip-flop 21of FIG. 2. Thus the output of flip-flop 31 is HIGH if the ignition hasjust been turned on and if a starting process has been triggered.

A slope detector 32 is fed a bit Z_ds that indicates whether a diagnosisof intake manifold pressure sensor 14 has been performed. If so, theoutput of slope detector 32 goes HIGH. The diagnosis of intake manifoldpressure sensor 14 may involve not only checking current pressure pshand stored starting value psh_sta, as explained in connection withmeasures /2/ and /3/ of FIG. 2. Instead, it may involve any alternativeor supplemental test with which the reliability performance of intakemanifold pressure sensor 14 may be checked.

Bit B_psidss indicated in FIG. 3 corresponds to the same bit that wasexplained in connection with measure /1/ of FIG. 2.

Also present in FIG. 3 is an OR element 33, to which aforementioned bitsB_elm and E_ds are fed. If there is a HIGH signal at one of the twoinputs of the OR element, this indicates that there is an error inconnection with intake manifold pressure sensor 14. The output of ORelement 33 is thus also HIGH. The result of subsequent inverter 34 isthat its output is LOW.

In the opposite case, i.e., if intake manifold pressure sensor 14 isoperational, the inputs of OR element 33 are LOW, so that its output islikewise LOW. The output of inverter 34 is thus HIGH.

The outputs of flip-flop 31, slope detector 32, inverter 34, and bitB_psidss are sent to an AND gate 35. If all four inputs of AND gate 35are HIGH, its output is also HIGH.

This is the case when i) the ignition of internal combustion engine 10is turned on again, ii) a starting process is triggered by control unit16, iii) a check of intake manifold pressure sensor 14 has beenperformed, iv) the release conditions explained in connection with FIG.2 have been fulfilled successfully, and v) intake manifold pressuresensor 14 is operational.

This is a second part of the aforementioned release conditions that maybe required to be fulfilled for the check of ambient pressure sensor 15to be performed. If the conditions are fulfilled and the output of ANDgate 35 is HIGH, this is detected by function 36 and is furtherprocessed as part of the measures identified with /1/, /2/, and /3/ inFIG. 3.

In measure /1/ a bit B_ppldsu, which indicates that the check of ambientpressure sensor 15 may take place, is set to “true=one.” This is thecase when all release conditions of FIG. 2 and all the above releaseconditions of FIG. 3 are fulfilled and the output of AND gate 35 isHIGH.

Measures /2/ and /3/ relate to the check of ambient pressure sensor 15.This check is explained below.

Control unit 16 uses signal DSU from ambient pressure sensor 15 toproduce an ambient pressure pu. Also present in control unit 16 is asignal puroh, which represents the ambient pressure that has not beenfiltered or checked for plausibility. In addition, control unit 16performs tests with which it determines whether signal DSU of ambientpressure sensor 15 is at all reasonable or plausible. The result of thistest is present as bit E_dsu.

Ambient pressure pu and signal puroh are fed to a selector switch 37,which is controlled by bit E_dsu. If bit E_dsu indicates that ambientpressure sensor 15 is delivering a plausible signal DSU, then ambientpressure pu obtained from ambient pressure sensor 15 is relayed byselector switch 37. If not, signal puroh is relayed.

We shall assume now that the first case exists, and that ambientpressure pu obtained from ambient pressure sensor 15 is thereforepresent at the output of selector switch 37.

Stored starting value psh_sta is subtracted from ambient pressure pu bya block 38, according to FIG. 3. The absolute value is determined fromthe difference by a block 39. This result is compared to a maximum valueDPMAX by a comparator 40. If the absolute value of the differencebetween ambient pressure pu and stored starting value psh_sta is greaterthan maximum value DPMAX, then the output of comparator 40 is HIGH.

Underlying the above procedure is the consideration, mentioned earlier,that starting value psh_sta measured by intake manifold pressure sensor14 before the starting process and then stored is approximately the sameas the ambient pressure. Thus if it is determined on the basis of therelease conditions that intake manifold pressure sensor 14 is notdefective, and that a correct starting process has taken place, thenafter this starting process ambient pressure pu obtained from ambientpressure sensor 15 must be approximately the same as stored startingvalue psh_sta.

At the same time, however, this indicates that the absolute value of thedifference between ambient pressure pu and starting value psh_sta mayonly be very small. This is checked through the comparison with maximumvalue DPMAX. If maximum value DPMAX is not exceeded, it is concludedthat ambient pressure sensor 15 is not defective. This is indicated by aLOW signal at the output of comparator 40. But if maximum value DPMAX isexceeded, a defect of ambient pressure sensor 15 is concluded, and theoutput of comparator 40 is HIGH.

In the case of a supercharged internal combustion engine 10, a startingvalue pll_Sta is also subtracted from ambient pressure pu by a block 41,according to FIG. 3. Starting value pll_sta is comparable to startingvalue psh_sta. Both starting values are measured prior to the startingprocess and then stored. Because the two starting values are measuredprior to the starting process, it is assumed that they are approximatelythe same as the ambient pressure. As explained earlier, starting valuepsh_sta is measured by intake manifold pressure sensor 14, whereasstarting value pll_sta is measured by a charge air pressure sensor,which is located inside the device that is used to charge internalcombustion engine 10.

The absolute value is determined by a block 42 from the differencebetween ambient pressure pu and stored starting value pll_sta. Thisresult is then compared by a comparator 43 to maximum value DPMAXmentioned earlier. If the absolute value of the difference betweenambient pressure pu and starting value pll_sta does not exceed maximumvalue DPMAX, it is concluded that ambient pressure sensor 15 isoperational, and the output of comparator 43 is LOW.

The outputs of comparator 40 and comparator 43 act on an AND gate 44. Ifboth of these outputs are HIGH, then the output of AND gate 44 is alsoHIGH.

It should be pointed out that the described check based on storedstarting value pll_sta, i.e., based on the charge air pressure of asupercharged internal combustion engine 10, represents a possibilitywhich may also be dispensed with. In that case, blocks 41, 42, 43, and44 are not present. It is also possible, in all of the functions andmeasures that were explained earlier or still remain to be explained inconnection with intake manifold pressure sensor 14, for this intakemanifold pressure sensor 14 to be replaced by the forenamed charge airpressure sensor. In that case, the charge air pressure sensor representsan alternative to intake manifold pressure sensor 14 in regard to thecheck of the ambient pressure sensor.

A HIGH signal at the output of AND gate 44 results in bits B_pldsu andB_drpldsu being set to “true=one.” This is equivalent to a defect inambient pressure sensor 15. If the output of AND gate 44 is LOW, theforenamed bits are set to “false=zero,” which signals the reliabilityperformance of ambient pressure sensor 15.

Bit B_pldsu is intended to be further processed by control unit 16. BitB_drpldsu is stored, and may be used for example in conjunction with aninspection or repair of internal combustion engine 10 to direct thetesting personnel to defective ambient pressure sensor 15.

Let it be pointed out again that measures /1/, /2/, and /3/ of FIG. 3are carried out only if the described release conditions of FIGS. 2 and3 are fulfilled and the output of AND gate 35 is HIGH.

If ambient pressure sensor 15 has been detected as defective, it ispossible to replace ambient pressure pu, itself obtained from ambientpressure sensor 15, in another manner. If intake manifold pressuresensor 14 has been recognized as operational, this may be accomplishedby continuing to use starting value psh_sta, i.e., the pressure inintake manifold 11 prior to the starting process, as a constant ambientpressure. This replacement of ambient pressure pu by starting valuepsh_sta may then be repeated after each starting process. If ambientpressure sensor 15 should be recognized as operational again, the abovereplacement may be canceled.

The described method maybe suitable not only for checking ambientpressure sensor 15, but in general for checking any pressure sensor thatcomes into contact with the environment of internal combustion engine10, at least before the latter is started. For example, a charge airpressure sensor or an air filter pressure sensor maybe suitable forsensing an ambient pressure before internal combustion engine 10 isstarted. This ambient pressure may then be compared (block 38) tostarting value psh_sta determined by intake manifold pressure sensor 14,in accordance with the above description. That may be used to reach aconclusion about the reliability performance of the charge air pressuresensor or the air filter pressure sensor (block 40).

1-13. (canceled)
 14. A method for operating an internal combustionengine, comprising: determining an ambient pressure via an ambientpressure sensor; determining a pressure in an intake manifold of theinternal combustion engine via an intake manifold pressure sensor;obtaining a starting value via the intake manifold pressure sensorbefore a starting process of the internal combustion engine; andchecking a reliability performance of the ambient pressure sensor bycomparing the ambient pressure to the starting value, wherein thecomparison is only performed if a preceding check of the intake manifoldpressure sensor yields a result that the intake manifold pressure sensoris operational.
 15. The method of claim 14, wherein the result of thecheck of the intake manifold pressure sensor only continues to be used,if one or more of the following release conditions are fulfilled: i) anignition of the internal combustion engine has just been turned on; ii)the starting process of the internal combustion engine has beentriggered; iii) an actual speed of the internal combustion engine iswithin a desired speed range; iv) a throttle valve of the internalcombustion engine is opened no wider than a maximum throttle valveangle; and v) the starting process has not yet exceeded a prescribedduration.
 16. The method of claim 14, wherein the check of the intakemanifold pressure sensor includes: detecting the starting value via theintake manifold pressure sensor before the starting process of theinternal combustion engine; storing the starting value; after thestarting process, comparing the starting value to the pressure in theintake manifold; and recognizing the intake manifold pressure sensor asoperational, if a difference of the starting value and the pressure inthe intake manifold exceeds a minimum value.
 17. The method of claim 14,wherein the comparison of the ambient pressure to the starting value isonly performed if one or more of the following release conditions arefulfilled: i) an ignition of the internal combustion engine has justbeen switched on; ii) the starting process has been triggered; iii) thecheck of the intake manifold pressure sensor has been performed; and iv)the intake manifold pressure sensor is operational.
 18. The method ofclaim 14, wherein a check of the ambient pressure sensor includes: oneof detecting and triggering the starting process of the internalcombustion engine; one of before and during the starting process,storing the intake manifold pressure detected by the intake manifoldpressure sensor as the starting value; comparing the stored startingvalue to the ambient pressure obtained from the ambient pressure sensor;and recognizing the ambient pressure sensor as operational, if thedifference of the starting value and the ambient pressure does notexceed a maximum value.
 19. The method of claim 18, further comprising:detecting a malfunction of the ambient pressure sensor when the storedstarting value is used as the ambient pressure.
 20. The method of claim14, wherein one of in addition to and alternatively to obtaining thestarting value from the intake manifold pressure sensor and storing thestarting value, the starting value is obtained from a charge-airpressure sensor and stored before the starting process is used.
 21. Amethod for operating an internal combustion engine, comprising:providing a pressure sensor in contact with an environment before astarting process of the internal combustion engine; determining acorresponding pressure via the pressure sensor; determining a pressurein an intake manifold of the internal combustion engine via an intakemanifold pressure sensor; and checking a reliability performance of thepressure sensor by comparing the pressure determined by the pressuresensor to a starting value that is obtained by the intake manifoldpressure sensor before the starting process of the internal combustionengine, wherein the comparison is only performed if a preceding check ofthe intake manifold pressure sensor yields the result that the intakemanifold pressure sensor is operational.
 22. The method of claim 21,wherein the pressure sensor includes one of an ambient pressure sensor,a charge air pressure sensor, and an air filter pressure sensor.
 23. Acomputer program product for use with a computer, the computer programproduct having program commands for performing a method for operating aninternal combustion engine, the method comprising: determining anambient pressure via an ambient pressure sensor; determining a pressurein an intake manifold of the internal combustion engine via an intakemanifold pressure sensor; obtaining a starting value via the intakemanifold pressure sensor before a starting processing of the internalcombustion engine; and checking a reliability performance of the ambientpressure sensor by comparing the ambient pressure to the starting value,wherein the comparison is only performed if a preceding check of theintake manifold pressure sensor yields a result that the intake manifoldpressure sensor is operational.
 24. The computer program product ofclaim 23, wherein the computer program product is stored on anelectronic storage medium.
 25. The computer program product of claim 23,wherein the computer program product is stored in a flash memory.
 26. Acontrol unit for an internal combustion engine, comprising: an ambientpressure sensor to determine an ambient pressure; an intake manifoldpressure sensor to determine a pressure in an intake manifold of theinternal combustion engine, the pressure including a starting valuedetermined before a starting process of the internal combustion engine;and an arrangement to check a reliability performance of the ambientpressure sensor by comparing the ambient pressure to the starting value,wherein the comparison is only performed if a preceding check of theintake manifold pressure sensor yields the result that the intakemanifold pressure sensor is operational.
 27. An internal combustionengine, comprising: an ambient pressure sensor to determine an ambientpressure; an intake manifold; an intake manifold pressure sensor todetermine a pressure in the intake manifold, the intake manifoldpressure sensor configured to obtain a starting value before a startingprocess of the internal combustion engine; and a control unit to check areliability performance of the ambient pressure sensor, the control unitconfigured to compare the ambient pressure to the starting value;wherein the comparison is only performed if a preceding check of thereliability performance of the intake manifold pressure sensor yields aresult that the intake manifold pressure sensor is operational.
 28. Theinternal combustion engine of claim 27, wherein the internal combustionengine is configured for a motor vehicle.